In the filtration processes previously described, the flow of broth was perpendicular to the filtration membrane.Consequently, blockage of the membrane led to lower rates of productivity and/or the need for filter aids to be added, and these were serious disadvantages.In contrast, an alternative which is rapidly gaining prominence both in the processing of whole fermentation broths and cell lysates is cross-flow filtration.Here, the flow of medium to be filtered is tangential to the membrane, and no filter cake builds up on the membrane.

The benefits of cross-flow filtration are:

(a) Efficient separation : 99.9% cell retention.(b) Closed system : For the containment of organisms with no aerosol formation.(c) Separation is independent of cell and media densities, in contrast to centrifugation.(d) No addition of filter aid.